Drug delivery devices, which allow multiple dosing of the required dosage of liquid drug and administration of the liquid to a patient, are well known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Pen-type injectors of this kind must meet a number of requirements to meet user needs. These devices need to be robust in construction, yet easy to use both in terms of the manipulation of the parts and understanding by a user of its operation. In the case of those with diabetes, many users will be physically infirm and may also have impaired vision. Where the injector is to be disposable rather than reusable, the injector should be cheap to manufacture and easy to dispose of (preferably being suitable for recycling).
WO 01/87386 A1 teaches a mechanical dose display for a medicine administration device consisting of at least one flexible disk which is driven by the dose setting actuator and which carries a band of numbers along its perimeter. By folding the disc in such a way that the diametrical opposite points of the perimeter just meet, allows each digit along the perimeter to be about three times as high as corresponding digits written on a drum having a diameter corresponding to the diameter of the tube formed by the folded disc. Through the addition of a second disc it is possible to show a two-digit number.
WO 98/10813 A1 discloses a dose setting mechanism by which doses are indicated on a clock dial having a first part secured to the housing and a second part which is rotatable relative to the first part and which is coupled to the dose setting element. One of the parts carries the scale and the other carries an indicating member indicating a point on the scale. By using a clock dial the dial can be made arbitrarily large being limited only by the fact that the device must not be too bulky.
U.S. Pat. No. 5,279,585 A discloses an injection device for injecting fluids such as insulin within body tissue. The dose setting means of the device includes a units counter ring, a tens counter ring positioned in adjoining relation to the units counter ring, and a transmission means connecting the units counter means and the tens counter ring.